'\" t
.TH "SD_BUS_MESSAGE_GET_COOKIE" "3" "" "systemd 257~rc3" "sd_bus_message_get_cookie"
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.SH "NAME"
sd_bus_message_get_cookie, sd_bus_message_get_reply_cookie \- Returns the transaction cookie of a message
.SH "SYNOPSIS"
.sp
.ft B
.nf
#include <systemd/sd\-bus\&.h>
.fi
.ft
.HP \w'int\ sd_bus_message_get_cookie('u
.BI "int sd_bus_message_get_cookie(sd_bus_message\ *" "message" ", uint64_t\ *" "cookie" ");"
.HP \w'int\ sd_bus_message_get_reply_cookie('u
.BI "int sd_bus_message_get_reply_cookie(sd_bus_message\ *" "message" ", uint64_t\ *" "cookie" ");"
.SH "DESCRIPTION"
.PP
\fBsd_bus_message_get_cookie()\fR
returns the transaction cookie of a message\&. The cookie uniquely identifies a message within each bus peer, but is not globally unique\&. It is assigned when a message is sent\&.
.PP
\fBsd_bus_message_get_reply_cookie()\fR
returns the transaction cookie of the message the specified message is a response to\&. When a reply message is generated for a method call message, its cookie is copied over into this field\&. Note that while every message that is transferred is identified by a cookie, only response messages carry a reply cookie field\&.
.PP
Both functions take a message object as first parameter and a place to store the 64\-bit cookie in\&.
.SH "RETURN VALUE"
.PP
On success, these calls return 0 or a positive integer\&. On failure, they return a negative errno\-style error code\&.
.PP
On success, the cookie/reply cookie is returned in the specified 64\-bit unsigned integer variable\&.
.SS "Errors"
.PP
Returned errors may indicate the following problems:
.PP
\fB\-EINVAL\fR
.RS 4
A specified parameter is invalid\&.
.RE
.PP
\fB\-ENODATA\fR
.RS 4
No cookie has been assigned to this message\&. This either indicates that the message has not been sent yet and hence has no cookie assigned, or that the message is not a method response message and hence carries a reply cookie field\&.
.RE
.SH "NOTES"
.PP
Functions described here are available as a shared library, which can be compiled against and linked to with the
\fBlibsystemd\fR\ \&\fBpkg-config\fR(1)
file\&.
.PP
The code described here uses
\fBgetenv\fR(3), which is declared to be not multi\-thread\-safe\&. This means that the code calling the functions described here must not call
\fBsetenv\fR(3)
from a parallel thread\&. It is recommended to only do calls to
\fBsetenv()\fR
from an early phase of the program when no other threads have been started\&.
.SH "HISTORY"
.PP
\fBsd_bus_message_get_cookie()\fR
and
\fBsd_bus_message_get_reply_cookie()\fR
were added in version 209\&.
.SH "SEE ALSO"
.PP
\fBsystemd\fR(1), \fBsd-bus\fR(3), \fBsd_bus_new\fR(3)
